Semiconductor device, electronic component, and electronic device

ABSTRACT

To provide a semiconductor device including a small-area circuit with high withstand voltage, an oxide semiconductor (OS) transistor is used as some of transistors included in a circuit handling an analog signal in a circuit to which high voltage is applied. The use of an OS transistor with high withstand voltage as a transistor requiring resistance to high voltage enables the circuit area to be reduced without lowering the performance, as compared to the case using a Si transistor. Furthermore, an OS transistor can be provided over a Si transistor, so that transistors using different semiconductor layers can be stacked, resulting in a much smaller circuit area.

BACKGROUND OF THE INVENTION 1. Field of the Invention

One embodiment of the present invention relates to a semiconductordevice, an electronic component, and an electronic device.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of the invention disclosed inthis specification and the like relates to an object, a method, or amanufacturing method. In addition, one embodiment of the presentinvention relates to a process, a machine, manufacture, or a compositionof matter. Specifically, examples of the technical field of oneembodiment of the present invention disclosed in this specificationinclude a semiconductor device, a display device, a light-emittingdevice, a power storage device, a memory device, a method for drivingany of them, and a method for manufacturing any of them.

2. Description of the Related Art

A driver circuit of a display device is required to have higherperformance to meet demand for multiple gray levels and higherdefinition of a display portion. Accordingly, an integrated circuit (IC,hereinafter also referred to as driver IC) is used as a driver circuitof a display device, particularly as a source driver (e.g., see PatentDocument 1).

A driver IC is roughly divided into two parts: a data retention unit forhandling a digital signal, such as a shift register and a latch, and agrayscale voltage generation unit such as a level shifter, adigital-to-analog converter (DAC) handling an analog signal, and ananalog buffer.

The data retention unit for handling a digital signal needs to operateat high speed; thus, a transistor included in the data retention unit isminutely processed and operates at low voltage. Meanwhile, the grayscalevoltage generation unit for handling an analog signal operates at highervoltage than the data retention unit to handle a voltage for driving adisplay portion.

REFERENCE

Patent Document 1: Japanese Published Patent Application No. 2007-286525

SUMMARY OF THE INVENTION

Since a circuit portion handling an analog signal operates at highervoltage than a circuit portion handling a digital signal as describedabove, a transistor included in the circuit portion handling an analogsignal is required to withstand higher voltage. To increase thewithstand voltage, the size of the transistor in the circuit portionhandling an analog signal is designed to be larger than that in thecircuit portion handling a digital signal.

However, the increase in the transistor size for achieving higherwithstand voltage leads to a larger circuit area. A reduction in size ofa display device is demanded, and accordingly a reduction in the circuitarea of a driver IC is required.

In view of the above, an object of one embodiment of the presentinvention is to provide a semiconductor device or the like with a novelstructure that includes a circuit with a small area. Another object ofone embodiment of the present invention is to provide a semiconductordevice or the like with a novel structure that includes a circuit withhigh withstand voltage. Another object of one embodiment of the presentinvention is to provide a novel semiconductor device or the like.

Note that the objects of one embodiment of the present invention are notlimited to the above. The objects described above do not disturb theexistence of other objects. The other objects are objects that are notdescribed above and will be described below. The other objects will beapparent from and can be derived from the description of thespecification, the drawings, and the like by those skilled in the art.One embodiment of the present invention is to achieve at least one ofthe above objects and the other objects.

One embodiment of the present invention is a semiconductor deviceincluding a first circuit, a second circuit, and a third circuit. Thefirst circuit receives a first signal and is capable of boosting a firstvoltage of the first signal into a second voltage. The second circuit iscapable of converting the first signal into a second signal. The thirdcircuit receives the second signal and is capable of amplifying a firstamount of current to a second amount of current and outputting thesecond amount of current. The second circuit includes a plurality ofwirings and a first transistor electrically connected to each of theplurality of wirings. The plurality of wirings are capable oftransmitting different voltages. The first transistor is capable ofoperating as a switch. The first transistor includes a semiconductorlayer containing an oxide semiconductor.

Another embodiment of the present invention is a semiconductor deviceincluding a first circuit, a second circuit, and a third circuit. Thefirst circuit receives a first signal and is capable of boosting a firstvoltage of the first signal into a second voltage. The second circuit iscapable of converting the first signal into a second signal. The thirdcircuit receives the second signal and is capable of amplifying a firstamount of current to a second amount of current and outputting thesecond amount of current. The second circuit includes a plurality ofwirings, a first transistor, and a second transistor. The plurality ofwirings include a first wiring capable of transmitting the firstvoltage, and a second wiring capable of transmitting the second voltagehigher than the first voltage. The first transistor is capable ofoperating as a switch. The second transistor is capable of operating asa switch. The first transistor includes a semiconductor layer containingan oxide semiconductor. The second transistor includes a semiconductorlayer containing silicon.

In the semiconductor device of one embodiment of the present invention,it is preferred that a channel region of the first transistor and achannel region of the second transistor partly overlap with each other.

In the semiconductor device of one embodiment of the present invention,it is preferred that the first circuit includes a third transistorelectrically connected to a wiring applying the first voltage, and afourth transistor electrically connected to a wiring applying the secondvoltage; and that the third transistor includes a semiconductor layercontaining silicon, and the fourth transistor includes a semiconductorlayer containing an oxide semiconductor.

Note that other embodiments of the present invention will be shown inEmbodiments 1 to 6 and the drawings.

One embodiment of the present invention can provide a semiconductordevice or the like with a novel structure that includes a circuit with asmall area. Accordingly, the size of the semiconductor device can besmall. Another embodiment of the present invention can provide asemiconductor device or the like with a novel structure that includes acircuit with high withstand voltage. Thus, the semiconductor device canhave high reliability. Another embodiment of the present invention canprovide a novel semiconductor device or the like.

Note that the effects of one embodiment of the present invention are notlimited to the above. The effects described above do not disturb theexistence of other effects. The other effects are effects that are notdescribed above and will be described below. The other effects will beapparent from and can be derived from the description of thespecification, the drawings, and the like by those skilled in the art.One embodiment of the present invention is to have at least one of theabove effects and the other effects. Accordingly, one embodiment of thepresent invention does not have the above effects in some cases.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a circuit block diagram illustrating one embodiment of thepresent invention;

FIG. 2 is a circuit block diagram illustrating one embodiment of thepresent invention;

FIG. 3 is a circuit block diagram illustrating one embodiment of thepresent invention;

FIG. 4 is a circuit diagram illustrating one embodiment of the presentinvention;

FIG. 5 is a circuit diagram illustrating one embodiment of the presentinvention;

FIG. 6 is a circuit diagram illustrating one embodiment of the presentinvention;

FIG. 7 is a circuit diagram illustrating one embodiment of the presentinvention;

FIG. 8 is a circuit diagram illustrating one embodiment of the presentinvention;

FIG. 9 is a circuit block diagram illustrating one embodiment of thepresent invention;

FIGS. 10A and 10B are circuit diagrams illustrating one embodiment ofthe present invention;

FIGS. 11A and 11B are cross-sectional TEM images of an oxidesemiconductor, and FIG. 11C shows local Fourier transform images of theoxide semiconductor;

FIGS. 12A and 12B show nanobeam electron diffraction patterns of oxidesemiconductor films, and FIGS. 12C and 12D illustrate an example of atransmission electron diffraction measurement apparatus;

FIG. 13A shows an example of structural analysis by transmissionelectron diffraction measurement, and FIGS. 13B and 13C are plan-viewTEM images;

FIG. 14 is a cross-sectional view illustrating one embodiment of thepresent invention;

FIGS. 15A and 15B are cross-sectional views each illustrating oneembodiment of the present invention;

FIG. 16A is a flowchart showing a fabrication process of an electroniccomponent, and FIG. 16B is a schematic cross-sectional view of theelectronic component;

FIGS. 17A and 17B each illustrate a display panel including anelectronic component;

FIG. 18 illustrates a display module including a display panel;

FIGS. 19A to 19E each illustrate an electronic device including anelectronic component;

FIG. 20 shows ID-VD curves for describing one embodiment of the presentinvention; and

FIGS. 21A and 21B show ID-VD curves for describing one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described below with reference to the drawings. Notethat the embodiments can be implemented with various modes, and it willbe readily appreciated by those skilled in the art that modes anddetails can be changed in various ways without departing from the spiritand scope of the present invention. Thus, the present invention shouldnot be interpreted as being limited to the following description of theembodiments.

In the drawings, the size, the layer thickness, or the region isexaggerated for clarity in some cases. Therefore, embodiments of thepresent invention are not limited to such a scale. Note that thedrawings are schematic views showing ideal examples, and embodiments ofthe present invention are not limited to shapes or values shown in thedrawings. For example, variation in signal, voltage, or current due tonoise or difference in timing can be included.

In this specification and the like, a transistor is an element having atleast three terminals: a gate, a drain, and a source. The transistor hasa channel region between the drain (a drain terminal, a drain region, ora drain electrode) and the source (a source terminal, a source region,or a source electrode), and current can flow through the drain, thechannel region, and the source.

Since the source and the drain of the transistor may change depending onthe structure, operating conditions, and the like of the transistor, itis difficult to define which is a source or a drain. Thus, it ispossible that a portion functioning as the source and a portionfunctioning as the drain are not called a source and a drain, and thatone of the source and the drain is referred to as a first electrode andthe other is referred to as a second electrode.

In this specification, ordinal numbers such as first, second, and thirdare used to avoid confusion among components, and thus do not limit thenumber of the components.

In this specification, the expression “A and B are connected” means thecase where A and B are electrically connected to each other in additionto the case where A and B are directly connected to each other. Here,the expression “A and B are electrically connected” means the case whereelectric signals can be transmitted and received between A and B when anobject having any electric action exists between A and B.

For example, any of the following expressions can be used for the casewhere a source (or a first terminal or the like) of a transistor iselectrically connected to X through Z1 (or by bypassing Z1) and a drain(or a second terminal or the like) of the transistor is electricallyconnected to Y through Z2 (or by bypassing Z2), or the case where asource (or a first terminal or the like) of a transistor is directlyconnected to one part of Z1 and another part of Z1 is directly connectedto X while a drain (or a second terminal or the like) of the transistoris directly connected to one part of Z2 and another part of Z2 isdirectly connected to Y.

Examples of the expressions include “X, Y, and a source (or a firstterminal or the like) and a drain (or a second terminal or the like) ofa transistor are electrically connected to each other such that X, thesource (or the first terminal or the like) of the transistor, the drain(or the second terminal or the like) of the transistor, and Y areelectrically connected to each other in this order”; “a source (or afirst terminal or the like) of a transistor is electrically connected toX, a drain (or a second terminal or the like) of the transistor iselectrically connected to Y, and X, the source (or the first terminal orthe like) of the transistor, the drain (or the second terminal or thelike) of the transistor, and Y are electrically connected to each otherin this order”; and “X is electrically connected to Y through a source(or a first terminal or the like) and a drain (or a second terminal orthe like) of a transistor, and X, the source (or the first terminal orthe like) of the transistor, the drain (or the second terminal or thelike) of the transistor, and Y are provided to be connected in thisorder”. When the connection order in a circuit structure is defined byan expression similar to the above examples, a source (or a firstterminal or the like) and a drain (or a second terminal or the like) ofa transistor can be distinguished from each other to specify thetechnical scope. Note that these expressions are only examples, andthere is no limitation on the expressions. Here, X, Y, Z1, and Z2 eachdenote an object (e.g., a device, an element, a circuit, a wiring, anelectrode, a terminal, a conductive film, or a layer).

In this specification, terms for explaining arrangement, such as overand under, are used for convenience to describe the positional relationbetween components with reference to drawings. The positional relationbetween components is changed as appropriate in accordance with adirection in which each component is described. Thus, the positionalrelation is not limited to that described with a term used in thisspecification and can be explained with another term as appropriatedepending on the situation.

The positional relation of circuit blocks in a block diagram isspecified for description. Even when a block diagram shows thatdifferent functions are achieved by different circuit blocks, onecircuit block may be actually configured to achieve different functions.Functions of circuit blocks in a diagram are specified for description,and even when a diagram shows one circuit block performing givenprocessing, a plurality of circuit blocks may be actually provided toperform the processing.

Embodiment 1

In this embodiment, examples of a circuit block diagram and a circuitdiagram of a semiconductor device functioning as a driver IC will bedescribed.

In this specification and the like, a semiconductor device means anydevice that can function by utilizing semiconductor characteristics;thus, a driver IC composed of semiconductor elements such as transistorsand a display device including the driver IC are included in thecategory of the semiconductor device.

FIG. 1 is a circuit block diagram that schematically illustrates asemiconductor device.

The semiconductor device illustrated in FIG. 1 includes a level shifterLS, a pass transistor logic PTL, and an amplifier AMP.

A semiconductor device functioning as a driver IC is roughly dividedinto two parts: a data retention unit for sampling and retaining aninput digital data signal, and a grayscale voltage generation unit forgenerating a grayscale voltage for a display portion on the basis of thedata signal. The level shifter LS, the pass transistor logic PTL, andthe amplifier AMP are included in the grayscale voltage generation unit.

Although not shown, the semiconductor device includes a data retentionunit in addition to the circuits in the grayscale voltage generationunit illustrated in FIG. 1. A digital data signal retained in the dataretention unit is input to the level shifter LS. This data signal isinput as a low-voltage signal so that the circuit portion handling adigital signal is driven at high speed.

The level shifter LS in FIG. 1 is a circuit with a function of boostingand outputting an input digital data signal, for example. The levelshifter LS boosts an input digital data signal into a high-voltagesignal and outputs the high-voltage signal because a circuit suppliedwith the signal output from the level shifter LS handles a voltage fordriving a display portion. The level shifter LS may be referred to as abooster circuit or simply as a circuit.

An example of the data signal input to the level shifter LS is digitalimage data. FIG. 1 illustrates data signals DATA[0]-DATA[k−1] (k is anatural number of 2 or more) as digital image data.

The level shifter LS includes a plurality of level shifterscorresponding to the number of input data signals. FIG. 1 illustrates anexample where level shifters LS[0]-LS[k−1] are provided. For example,the first level shifter LS[0] boosts an input data signal DATA[0] andoutputs the resulting signal as a signal DATA[0]_LS. The same applies tothe second and subsequent level shifters LS[1]-LS[k−1].

In the following description, the data signals DATA[0]-DATA[k−1] inputto the level shifter LS are signals with a voltage amplitude of V1/VSS,and data signals DATA[0]_LS-DATA[k−1]_LS output from the level shifterLS are signals boosted to have a voltage amplitude of V2/VSS (V2>V1).

Note that “V1/VSS” means that the voltage amplitude ranges from a highpower supply potential V1 to a low power supply potential VSS, and“V2/VSS” means that the voltage amplitude ranges from a high powersupply potential V2 to the low power supply potential VSS. Note that thelow power supply potential VSS may be a ground potential GND.

The pass transistor logic PTL illustrated in FIG. 1 is a circuit havinga function of converting an input digital signal into an analog signal,for example. A data signal input to the pass transistor logic PTL is adigital signal, and the digital data signal is converted into an analogsignal by the pass transistor logic PTL. The pass transistor logic PTLmay be referred to as a digital-to-analog (D/A) converter circuit orsimply as a circuit.

The pass transistor logic PTL includes transistors 11. The on/off statesof the transistors 11 are controlled by the respective data signalsDATA[0]_LS-DATA[k−1]_LS which are boosted by the level shifter LS. Thetransistor 11 functions as a switch.

A voltage of a data signal that is obtained by converting a digitalsignal into an analog signal by controlling the on/off state of thetransistor 11 included in the pass transistor logic PTL corresponds to agrayscale voltage for the display portion. Although the voltage levelvaries depending on display elements included in pixels of the displayportion, the voltage (V2/VSS) of an analog data signal needs to behigher than the voltage (V1/VSS) of a digital data signal for drivingthe data retention unit in the driver IC. Thus, in the level shifter LS,a voltage required to operate a switch for generating a voltage of ananalog data signal is converted into the voltage (V2/VSS), which ishigher than the voltage (V1/VSS) for driving the data retention unit inthe driver IC.

The pass transistor logic PTL is supplied with a plurality of voltagesV[0]-V[j−1] as well as the data signals DATA[0]_LS-DATA[k−1]_LS whichare boosted by the level shifter LS. The data signalsDATA[0]_LS-DATA[k−1]_LS are supplied to gates of the transistors 11. Thevoltages V[0]-V[j−1] are supplied to sources or drains of thetransistors 11. In accordance with the on/off state of the transistors11, the pass transistor logic PTL can output an output signal PTL_OUTthat is an analog signal corresponding to the voltages V[0]-V[j−1].

The amplifier AMP illustrated in FIG. 1 is a circuit having a functionof increasing (amplifying) the amount of current to be output by makingthe voltage of an input signal and that of an output signal the same,for example. That is, the amplifier AMP has a function of outputting asignal with an increasing amount of current. The amplifier AMP includesa voltage follower VF to which the output signal PTL_OUT is input. Theamplifier AMP may be referred to as an amplification circuit or simplyas a circuit.

A signal input to the amplifier AMP is the analog output signal PTL_OUT.The amplifier AMP amplifies a first amount of current of the outputsignal PTL_OUT to a second amount of current of an analog data signalVdata and outputs the analog data signal Vdata. The data signal Vdataoutput from the amplifier AMP is a signal obtained by conversion into ananalog signal based on the digital data signals DATA[0]-DATA[k−1].

In the semiconductor device serving as the driver IC in FIG. 1, the datasignals DATA[0]-DATA[k−1] that are input as digital signals areconverted into the analog data signal Vdata and the data signal Vdata isoutput to a pixel in the display portion. A display element in the pixelneeds a voltage higher than a voltage for driving the driver IC;consequently, the on/off state of a transistor on the output side of thedriver IC is controlled with higher voltage than that on the input sideto obtain a signal with an intended voltage. For example, a transistoron the input side of the driver IC is controlled at a low voltage ofapproximately 2 V to 3 V for high-speed control, whereas a transistor onthe output side of the driver IC needs to be controlled at a highvoltage of approximately 5 V to 10 V.

In the configuration of the semiconductor device in one embodiment ofthe present invention, a transistor that uses silicon for asemiconductor layer serving as a channel formation region (hereinafterreferred to as Si transistor) and requires resistance to high voltage isreplaced with a transistor with resistance to high voltage.Specifically, in the configuration in FIG. 1, the transistor included inthe pass transistor logic PTL, which requires resistance to high voltagein the driver IC, is replaced with a transistor using an oxidesemiconductor for a semiconductor layer serving as a channel formationregion (hereinafter referred to as OS transistor).

The semiconductor device in FIG. 1 includes the level shifter LS, thepass transistor logic PTL, and the amplifier AMP and selectively uses OStransistors as transistors requiring high withstand voltage in each ofthe circuits, whereby the circuits in the semiconductor device can havea smaller area than those using only Si transistors with large L.Moreover, the OS transistors contain a semiconductor with a wider bandgap than that of a Si transistor, thus, the transistors in the driver ICcan have high withstand voltage without increasing in size. As a result,a highly reliable semiconductor device can be provided.

Note that L refers to channel length and means a length in the directionin which carriers move at the shortest distance between a pair ofimpurity regions serving as a source region and a drain region. Inaddition, W refers to channel width and means a width in the directionperpendicular to the channel length direction.

If a Si transistor is used as a transistor that requires high withstandvoltage in the pass transistor logic PTL, the circuit needs to bedesigned using a larger channel length to secure resistance to highvoltage. An increase in the number of Si transistors with a largerchannel length results in an increase in the circuit area.

On the other hand, when an OS transistor is used in the pass transistorlogic PTL, resistance to high voltage is obtained without increasing thechannel length in circuit design. A semiconductor layer serving as achannel formation region of the OS transistor can be formed usingIn—Ga—Zn-based oxide, for example. Since the band gap of In—Ga—Zn-basedoxide is wider than that of silicon by approximately 1 eV to 2 eV,application of high voltage to the OS transistor is less likely to causeavalanche breakdown, that is, the OS transistor is highly resistant tohigh voltage. Thus, dielectric breakdown is unlikely to occur in the OStransistor, and transistor defects can be suppressed in a semiconductordevice including OS transistors.

In the configuration in FIG. 1, OS transistors are used as thetransistors 11 in the pass transistor logic PTL that are supplied withthe data signals DATA[0]_LS-DATA[k−1]_LS which are boosted by the levelshifter LS. This configuration can reduce the circuit area as comparedto a configuration in which Si transistors with a larger channel lengthare used for circuit design to increase resistance to high voltage.Thus, the size of the semiconductor device can be decreased.

FIG. 20 shows ID-VD curves of a Si transistor and an OS transistor forexplaining drain breakdown voltage of the OS transistor. In FIG. 20, tocompare resistance to high voltage between the Si transistor and the OStransistor under the same conditions, both of the transistors have achannel length of 0.9 μm, a channel width of 10 μm, and a thickness of agate insulating film using silicon oxide of 20 nm. Note that the gatevoltage is 2 V.

As shown in FIG. 20, avalanche breakdown occurs in the Si transistor ata drain voltage of approximately 4 V, whereas in the OS transistor, aconstant current can flow until a drain voltage of approximately 26 Vcauses avalanche breakdown.

FIG. 21A shows ID-VD curves of an OS transistor with varying gatevoltage. FIG. 21B shows ID-VD curves of a Si transistor with varyinggate voltage. In FIGS. 21A and 21B, to compare resistance to highvoltage between the Si transistor and the OS transistor under the sameconditions, both of the transistors have a channel length of 0.9 μm, achannel width of 10 μm, and a thickness of a gate insulating film usingsilicon oxide of 20 nm. The gate voltage changes from 0.1 V to 2.06 V,4.02 V, 5.98 V, and 7.94 V in the OS transistor of FIG. 21A, and changesfrom 0.1 V to 1.28 V, 2.46 V, 3.64 V, and 4.82 V in the Si transistor ofFIG. 21B.

As shown in FIG. 21B, avalanche breakdown occurs in the Si transistor ata drain voltage of approximately 4 V to 5V, whereas in the OStransistor, a constant current can flow at a drain voltage ofapproximately 9 V without causing avalanche breakdown as shown in FIG.21A.

As seen from FIG. 20 and FIGS. 21A and 21B, the OS transistor has higherresistance to high voltage than the Si transistor; thus, dielectricbreakdown is unlikely to occur in the OS transistor, and transistordefects can be suppressed in a semiconductor device including OStransistors.

The OS transistor can be stacked over the Si transistor and thus issuitable to further reduce the area of the pass transistor logic PTL. Inaddition, the OS transistor can be stacked over another OS transistor,which is suitable for further area reduction of the pass transistorlogic PTL.

Note that in the circuit diagrams, “OS” is used to denote an OStransistor and “Si” is used to denote a Si transistor.

The OS transistor used in the configuration of FIG. 1 can exhibitultra-low off-state current.

The off-state current of an OS transistor can be reduced by reducing theconcentration of impurities in an oxide semiconductor to make the oxidesemiconductor intrinsic or substantially intrinsic. The term“substantially intrinsic” refers to a state where an oxide semiconductorhas a carrier density lower than 1×10¹⁷/cm³, preferably lower than1×10¹⁵/cm³, further preferably lower than 1×10¹³/cm³. In the oxidesemiconductor, hydrogen, nitrogen, carbon, silicon, and metal elementsother than main components are impurities. For example, hydrogen andnitrogen form donor levels to increase the carrier density.

A transistor using an intrinsic or substantially intrinsic oxidesemiconductor has a low carrier density and thus is less likely to havenegative threshold voltage. Moreover, because of few carrier traps inthe oxide semiconductor, the transistor using the oxide semiconductorhas small variation in electrical characteristics and high reliability.Furthermore, the transistor using the oxide semiconductor achievesultra-low off-state current.

For example, the OS transistor with reduced off-state current canexhibit a normalized off-state current per micrometer in channel widthof 1×10⁻¹⁸ A or less, preferably 1×10⁻²¹ A or less, more preferably1×10⁻²⁴ A or less at room temperature (approximately 25° C.), or 1×10⁻¹⁵A or less, preferably 1×10⁻¹⁸ A or less, more preferably 1×10⁻²¹ A orless at 85° C.

Note that the off-state current is a current that flows between a sourceand a drain when a transistor is off. For example, the off-state currentof an n-channel transistor with a threshold voltage of about 0 V to 2 Vrefers to a current that flows between a source and a drain when anegative voltage is applied between a gate and the source.

Since the OS transistor exhibits ultra-low off-state current asdescribed above, the use of the OS transistor in the pass transistorlogic PTL enables the amount of current that flows slightly through thetransistor in the off state to be extremely small. Thus, currentconsumption is decreased, resulting in lower power consumption of thesemiconductor device.

Although FIG. 1 illustrates the configuration in which all thetransistors in the pass transistor logic PTL are OS transistors, onlysome of them may be OS transistors.

FIG. 2 illustrates an example of a configuration using OS transistors assome of the transistors in the pass transistor logic PTL.

In FIG. 2, input data signals are denoted by DATA[0]-DATA[2(k−1)], andDATA[0]-DATA[k−1] are high order bits and DATA[k]-DATA[2(k−1)] are loworder bits. In the pass transistor logic PTL with the configuration inFIG. 2, a transistor to which a voltage based on a high order bit isapplied is a Si transistor, and a transistor to which a voltage based ona low order bit is applied is an OS transistor.

In the pass transistor logic PTL, a higher voltage is applied to thetransistor supplied with a voltage based on a high order bit than to thetransistor supplied with a voltage based on a low order bit. In FIG. 2,a plurality of voltages applied to the pass transistor logic PTL areshown as voltages V[0]-V[2(j−1)], where V[0]<V[2(j−1)].

In FIG. 2, transistors 12 supplied with DATA[0]_LS-DATA[k−1]_LS obtainedby boosting high order bits of data signals are p-channel Sitransistors. The transistors 11 supplied with DATA[k]_LS-DATA[2(k−1)]_LSobtained by boosting DATA[k]-DATA[2(k−1)] corresponding to low orderbits of data signals are OS transistors. Since DATA[0]_LS-DATA[k−1]_LSapplied as high order bits are signals supplied to the p-channel Sitransistors 12, signals with inverted logic levels of the digitalsignals are supplied.

With the configuration in FIG. 2, a voltage applied between a gate andsource (hereinafter Vgs) of each transistor included in the passtransistor logic PTL can be increased. Thus, the on/off state of thetransistor can be controlled without making a voltage (V2/VSS) boostedby the level shifter LS higher than the voltages V[0]-V[2(j−1)]. As aresult, even though small transistors are used in the pass transistorlogic PTL, the transistors secure resistance to high voltage, and thecircuit area can be reduced.

The pass transistor logic PTL including a Si transistor and an OStransistor is suitable to further reduce the circuit area because the OStransistor and the Si transistor can be closely stacked. Furthermore,the OS transistor can be stacked over another OS transistor, which issuitable for further reduction in the circuit area.

As another configuration example, the transistors included in the passtransistor logic PTL may be transistors 11BG having a backgate (alsoreferred to as second gate) as illustrated in FIG. 3.

When the transistors in the pass transistor logic PTL are thetransistors 11BG with a backgate, the area of a semiconductor layer towhich an electric field is applied can be increased even with the samecircuit area. Accordingly, even when the transistors are designed to fita smaller circuit area, the pass transistor logic PTL can operatewithout reducing the amount of current flowing through the transistors.

In the configuration of FIG. 1, an OS transistor can be used as some ofthe transistors in the level shifter LS.

FIG. 4 illustrates an example of a specific circuit configuration of thelevel shifter LS, here the level shifter LS[0]. The level shifter LSincludes transistors 21 to 30. The transistors 21 and 22 and thetransistors 23 and 24 that serve as inverters are supplied with thevoltage V1/VSS. The transistors 25 to 30 serving as a buffer aresupplied with the voltage V2/VSS.

Note that DATAB[0]_LS illustrated in FIG. 4 is a signal obtained byinverting the logic level of DATA[0]_LS.

In the level shifter LS, an OS transistor is provided as at least one ofthe transistors 25 to 30, which function as a buffer and are providedbetween wirings for supplying the voltage V2/VSS. In the exampleillustrated in FIG. 4, the transistors 27 and 30 are OS transistors andthe other transistors are Si transistors.

The semiconductor device with the configuration of FIG. 4 can have asmaller circuit area than a semiconductor device using Si transistorswith large L in the level shifter LS as well as in the pass transistorlogic PTL. In addition, power consumption of the semiconductor devicecan be reduced because current consumed when the OS transistors are offis suppressed.

In the configuration of FIG. 1, an OS transistor can be used in theamplifier AMP.

FIG. 5 illustrates an example of a specific circuit configuration of thevoltage follower VF included in the amplifier AMP. The voltage followerVF includes transistors 31 to 46, capacitors 47 and 48, and transistors49 and 50. The voltage follower VF is roughly divided into three parts:a differential input unit having the transistors 31 to 34, an amplifierunit having the transistors 35 to 46 and the capacitors 47 and 48, and abuffer unit having the transistors 49 and 50.

The voltage follower VF is supplied with the voltage V2/VSS. Note thatthe voltage follower VF may be supplied with voltages different from thevoltage V2/VSS, which are applied to the pass transistor logic PTL. Forexample, the voltage follower VF may be supplied with voltages V3 andVSS; the voltage V3 is higher than the voltage V2. The voltage followerVF is also supplied with bias voltages VB1 to VB6.

In the example illustrated in FIG. 5, the transistors 31 to 34, 39, 41,43 to 46, and 50 are OS transistors and the other transistors are Sitransistors.

The semiconductor device with the configuration of FIG. 5 can have asmaller circuit area than a semiconductor device using Si transistorswith large L in the voltage follower VF as well as in the passtransistor logic PTL. Moreover, power consumption of the semiconductordevice can be reduced because current consumed when the OS transistorsare off is suppressed.

In the voltage follower VF, an output voltage changes with thresholdvoltage variation in the transistors. The output voltage of the voltagefollower VF is a voltage for outputting a grayscale voltage for thedisplay portion, and preferably changes as little as possible becausehuman eyes are sensitive to grayscale deviation. Since the thresholdvoltage is controlled by impurity element addition or the like moreeasily in a Si transistor than in an OS transistor, it may be preferablethat some of the OS transistors in FIG. 5 be Si transistors.

For example, OS transistors are preferably used as transistors to whichhigh voltage is relatively less likely to be applied in the voltagefollower VF. For instance, the transistors 31, 32, 33, 39, 41, 43, 45,and 50 are OS transistors and the other transistors are Si transistorsas illustrated in FIG. 6. With this configuration, an output voltage ofthe voltage follower VF is less likely to be affected by thresholdvoltage variation in the transistors, so that an output voltage with anintended value is obtained.

Note that the voltages V[0]-V[j−1] described using FIG. 1, which areapplied to the pass transistor logic PTL, are generated by a voltagegenerator circuit composed of resistors connected in series.

A voltage generator circuit V-gene illustrated in FIG. 7 is an exampleof a circuit including a plurality of resistors 51 for generating thevoltages V[0]-V[j−1]. In the voltage generator circuit V-gene in FIG. 7,the resistors 51 are provided in series between wirings for supplyingthe voltage V2/VSS. The voltages V[0]-V[j−1] are obtained by dividingthe voltage V2/VSS using the resistors 51.

FIG. 7 illustrates a configuration example of the pass transistor logicPTL in addition to a configuration example of the voltage generatorcircuit V-gene. The pass transistor logic PTL with the configuration inFIG. 7 can generate a plurality of voltages that are smaller in numberthan data signals. Consequently, the number of transistors in the passtransistor logic PTL can be reduced.

When an n-channel OS transistor is provided close to a wiring forsupplying the high power supply potential, a voltage that is reduced bythe threshold voltage of the transistor is output. For this reason,among the transistors supplied with the voltages V[0]-V[j−1], ap-channel transistor is used as a transistor connected to a wiring thatis much affected by a reduction in threshold voltage, whereas ann-channel OS transistor is used as a transistor connected to a wiringthat is less affected by a reduction in threshold voltage. Thisconfiguration can reduce the circuit area, increase resistance to highvoltage, and almost eliminate the influence of the threshold voltage onthe output voltage.

In the configuration of FIG. 7, an OS transistor and a Si transistor maybe selectively used as illustrated in FIG. 8 depending on whether a datasignal supplied to each transistor is a high order bit or a low orderbit as described with FIG. 2.

With the configuration in FIG. 8, Vgs of each transistor included in thepass transistor logic PTL can be increased. Thus, the on/off state ofthe transistor can be controlled without making a voltage (V2/VSS)boosted by the level shifter LS higher than the voltages V[0]-V[2(j−1)].As a result, even though small transistors are used in the passtransistor logic PTL, the transistors secure resistance to high voltage,and the circuit area can be reduced.

The pass transistor logic PTL including a Si transistor and an OStransistor is suitable to further reduce the circuit area because the OStransistor and the Si transistor can be closely stacked. Furthermore,the OS transistor can be stacked over another OS transistor, which issuitable for further reduction in the circuit area.

As described above, the driver with the configuration in FIG. 1 includesthe level shifter LS, the pass transistor logic PTL, and the amplifierAMP and selectively uses OS transistors as transistors requiring highwithstand voltage in each of the circuits, whereby the circuits in thesemiconductor device can have a smaller area than those using only Sitransistors with large L. Moreover, the OS transistors contain asemiconductor with a wider band gap than that of a Si transistor, thus,the transistors in the driver can have high withstand voltage withoutincreasing in size. As a result, a highly reliable semiconductor devicecan be provided.

This embodiment can be implemented in appropriate combination with anyof the other embodiments.

Embodiment 2

This embodiment will explain a circuit block diagram of a display deviceincluding the level shifter LS, the pass transistor logic PTL, and theamplifier AMP, which are described in Embodiment 1. FIG. 9 is a circuitblock diagram illustrating a source driver, a gate driver, and a displayportion.

The display device in the circuit block diagram of FIG. 9 includes asource driver 100, a gate driver 101, and a display portion 102. In FIG.9, a pixel 103 is shown in the display portion 102.

The source driver 100 can have the driver IC described in Embodiment 1.Specifically, the source driver 100 includes a shift register SR, a datalatch D-Latch, the level shifter LS, the pass transistor logic PTL, thevoltage generator circuit V-gene, and the amplifier AMP. The sourcedriver 100 has a function of outputting an analog data signal to sourcelines SL[0]-SL[n−1] (n is a natural number of 2 or more).

The shift register SR receives a source clock SCLK and a source startpulse SSP, for example. The shift register SR generates a sampling pulseand outputs it to the data latch D-Latch.

In addition to the sampling pulse, the data signals DATA[0]-DATA[k−1],which are digital image data, are input to the data latch D-Latch. Thedata signals DATA[0]-DATA[k−1] are latched into the data latch D-Latchin response to the sampling pulse. The data latch D-Latch outputs thelatched data signals DATA[0]-DATA[k−1] to the level shifter LS.

The level shifter LS is as described in Embodiment 1. Specifically, thelevel shifter LS boosts the input signals DATA[0]-DATA[k−1] and outputsthe signals DATA[0]_LS-DATA[k−1]_LS.

The pass transistor logic PTL is as described in Embodiment 1.Specifically, the pass transistor logic PTL controls the on/off state ofthe transistors in accordance with the boosted signalsDATA[0]_LS-DATA[k−1]_LS and outputs the output signals PTL_OUT that areanalog signals corresponding to the voltages V[0]-V[j−1] generated inthe voltage generator circuit V-gene.

The amplifier AMP is as described in Embodiment 1. Specifically, theamplifier AMP increases the amount of current of the output signalPTL_OUT input thereto and outputs the data signal Vdata with anincreasing current.

The data signals Vdata obtained in the amplifier AMP are analog signalsoutput to the source lines SL[0]-SL[n−1].

The gate driver 101 includes a shift register and a buffer, for example.The gate driver 101 receives a gate start pulse, a gate clock signal,and the like and outputs a pulse signal. A circuit included in the gatedriver 101 may be an IC as in the source driver 100 or may be formedusing a transistor similar to that in the pixel 103 of the displayportion 102.

The gate driver 101 outputs scan signals to gate lines GL[0]-GL[m−1] (inis a natural number of 2 or more). Note that a plurality of gate drivers101 may be provided to separately control the gate lines GL[0]-GL[m−1].

In the display portion 102, the gate lines GL[0]-GL[m−1] and the sourcelines SL[0]-SL[n−1] are provided to intersect at substantially rightangles. The pixel 103 is provided at the intersection of the gate lineand the source line. For color display, the pixels 103 corresponding tothe respective colors of red, green, and blue (RGB) are arranged insequence in the display portion 102. Note that the pixels of RGB can bearranged in a stripe pattern, a mosaic pattern, a delta pattern, or thelike as appropriate. Without limitation to RGB, white, yellow, or thelike may be added to RGB for color display.

Configuration examples of the pixel 103 are illustrated in FIGS. 10A and10B.

A pixel 103A in FIG. 10A is an example of a pixel included in a liquidcrystal display device and includes a transistor 111, a capacitor 112,and a liquid crystal element 113.

The transistor 111 serves as a switching element for controlling theconnection between the liquid crystal element 113 and the source lineSL. The on/off state of the transistor 111 is controlled by a scansignal supplied to its gate through the gate line GL.

The capacitor 112 is an element formed by stacking conductive layers,for example.

The liquid crystal element 113 includes a common electrode, a pixelelectrode, and a liquid crystal layer, for example. Alignment of theliquid crystal material of the liquid crystal layer is changed by theaction of an electric field generated between the common electrode andthe pixel electrode.

A pixel 103B in FIG. 10B is an example of a pixel included in an ELdisplay device and includes a transistor 121, a transistor 122, and anEL element 123. FIG. 10B illustrates a power supply line VL in additionto the gate line GL and the source line SL. The power supply line VL isa wiring for supplying current to the EL element 123.

The transistor 121 serves as a switching element for controlling theconnection between a gate of the transistor 122 and the source line SL.The on/off state of the transistor 121 is controlled by a scan signalsupplied to its gate through the gate line GL.

The transistor 122 has a function of controlling current flowing betweenthe power supply line VL and the EL element 123, in accordance withvoltage applied to the gate of the transistor 122.

The EL element 123 is, for example, an element including alight-emitting layer provided between electrodes. The luminance of theEL element 123 can be controlled by the amount of current that flowsthrough the light-emitting layer.

The above circuit block diagram of the display device includes the levelshifter LS, the pass transistor logic PTL, and the amplifier AMPdescribed in Embodiment 1; thus, the circuit area of the source drivercan be small as in Embodiment 1. Consequently, the size of the displaydevice can be reduced. Moreover, according to one embodiment of thepresent invention, the transistors in the source driver can have highwithstand voltage; thus, a highly reliable semiconductor device can beprovided.

This embodiment can be implemented in appropriate combination with anyof the other embodiments.

Embodiment 3

This embodiment will explain an oxide semiconductor layer that can beused as a semiconductor layer of the transistor with low off-statecurrent described in the foregoing embodiment.

An oxide semiconductor used for a channel formation region in thesemiconductor layer of the transistor preferably contains at leastindium (In) or zinc (Zn). In particular, the oxide semiconductorpreferably contains both In and Zn. The oxide semiconductor preferablycontains a stabilizer for strongly bonding oxygen, in addition to In andZn. The oxide semiconductor preferably contains at least one of gallium(Ga), tin (Sn), zirconium (Zr), hafnium (Hf), and aluminum (Al) as thestabilizer.

As another stabilizer, the oxide semiconductor may contain one or morekinds of lanthanoid such as lanthanum (La), cerium (Ce), praseodymium(Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd),terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb), and lutetium (Lu).

As the oxide semiconductor used for the semiconductor layer of thetransistor, any of the following can be used, for example: indium oxide,tin oxide, zinc oxide. In—Zn-based oxide, Sn—Zn-based oxide, Al—Zn-basedoxide, Zn—Mg-based oxide, Sn—Mg-based oxide, In—Mg-based oxide,In—Ga-based oxide, In—Ga—Zn-based oxide (also referred to as IGZO),In—Al—Zn-based oxide, In—Sn—Zn-based oxide, Sn—Ga—Zn-based oxide,Al—Ga—Zn-based oxide, Sn—Al—Zn-based oxide, In—Hf—Zn-based oxide,In—Zr—Zn-based oxide, In—Ti—Zn-based oxide, In—Sc—Zn-based oxide,In—Y—Zn-based oxide, In—La—Zn-based oxide, In—Ce—Zn-based oxide,In—Pr—Zn-based oxide, In—Nd—Zn-based oxide, In—Sm—Zn-based oxide,In—Eu—Zn-based oxide, In—Gd—Zn-based oxide, In—Tb—Zn-based oxide,In—Dy—Zn-based oxide, In—Ho—Zn-based oxide, In—Er—Zn-based oxide,In—Tm—Zn-based oxide, In—Yb—Zn-based oxide, In—Lu—Zn-based oxide,In—Sn—Ga—Zn-based oxide, In—Hf—Ga—Zn-based oxide, In—Al—Ga—Zn-basedoxide, In—Sn—Al—Zn-based oxide, In—Sn—Hf—Zn-based oxide, andIn—Hf—Al—Zn-based oxide.

For example, an In—Ga—Zn-based oxide with an atomic ratio ofIn:Ga:Zn=1:1:1, 3:1:2, or 2:1:3 or an oxide with an atomic ratio closeto the above atomic ratios can be used.

If an oxide semiconductor film forming the semiconductor layer containsa large amount of hydrogen, the hydrogen and the oxide semiconductor arebonded to each other, so that part of the hydrogen serves as a donor andcauses generation of an electron which is a carrier. As a result, thethreshold voltage of the transistor shifts in the negative direction. Itis therefore preferable that after formation of the oxide semiconductorfilm, dehydration treatment (dehydrogenation treatment) be performed toremove hydrogen or moisture from the oxide semiconductor film so thatthe oxide semiconductor film is highly purified to contain impurities aslittle as possible.

Note that oxygen in the oxide semiconductor film is sometimes reduced bythe dehydration treatment (dehydrogenation treatment). For this reason,it is preferable that oxygen be added to the oxide semiconductor film tofill oxygen vacancies increased by the dehydration treatment(dehydrogenation treatment). In this specification and the like,supplying oxygen to an oxide semiconductor film may be expressed asoxygen adding treatment. Moreover, treatment for making the oxygencontent of an oxide semiconductor film be in excess of that in thestoichiometric composition may be expressed as treatment for making anoxygen-excess state.

In this manner, hydrogen or moisture is removed from the oxidesemiconductor film by the dehydration treatment (dehydrogenationtreatment) and oxygen vacancies therein are filled by the oxygen addingtreatment, whereby the oxide semiconductor film can be turned into ani-type (intrinsic) oxide semiconductor film or a substantially i-type(intrinsic) oxide semiconductor film that is extremely close to ani-type oxide semiconductor film. Note that “substantially intrinsic”means that the oxide semiconductor film contains extremely few (close tozero) carriers derived from a donor and has a carrier density of1×10¹⁷/cm³ or lower, 1×10¹⁶/cm³ or lower, 1×10¹⁵/cm³ or lower,1×10¹⁴/cm³ or lower, or 1×10¹³/cm³ or lower.

The transistor including an i-type or substantially i-type oxidesemiconductor film can have extremely favorable off-state currentcharacteristics. For example, the off-state drain current of thetransistor including the oxide semiconductor film can be 1×10⁻¹⁸ A orless, preferably 1×10⁻²¹ A or less, more preferably 1×10⁻²⁴ A or less atroom temperature (approximately 25° C.), or 1×10⁻¹⁵ A or less,preferably 1×10⁻¹⁸ A or less, more preferably 1×10⁻²¹ A or less at 85°C. Note that the off state of an n-channel transistor refers to a statewhere a gate voltage is sufficiently lower than the threshold voltage.Specifically, the transistor is off when the gate voltage is lower thanthe threshold voltage by 1 V or higher, 2 V or higher, or 3 V or higher.

The oxide semiconductor film may contain one or more of an oxidesemiconductor having a single crystal structure (hereinafter referred toas single crystal oxide semiconductor), an oxide semiconductor having apolycrystalline structure (hereinafter referred to as polycrystallineoxide semiconductor), an oxide semiconductor having a microcrystallinestructure (hereinafter referred to as microcrystalline oxidesemiconductor), and an oxide semiconductor having an amorphous structure(hereinafter referred to as amorphous oxide semiconductor). The oxidesemiconductor film may be a c-axis aligned crystalline oxidesemiconductor (CAAC-OS) film. Furthermore, the oxide semiconductor filmmay contain an amorphous oxide semiconductor and an oxide semiconductorhaving a crystal grain. A CAAC-OS and a microcrystalline oxidesemiconductor are described below as typical examples.

First, a CAAC-OS film is described.

The CAAC-OS film is an oxide semiconductor film having a plurality ofc-axis aligned crystal parts.

In a transmission electron microscope (TEM) image of the CAAC-OS film, aboundary between crystal parts, that is, a grain boundary is not clearlyobserved. Thus, in the CAAC-OS film, a reduction in electron mobilitydue to the grain boundary is less likely to occur.

According to the TEM image of the CAAC-OS film observed in a directionsubstantially parallel to a sample surface (cross-sectional TEM image),metal atoms are arranged in a layered manner in the crystal parts. Eachmetal atom layer reflects unevenness of a surface over which the CAAC-OSfilm is formed (hereinafter such a surface is referred to as a formationsurface) or a top surface of the CAAC-OS film, and is arranged parallelto the formation surface or the top surface of the CAAC-OS film.

On the other hand, according to the TEM image of the CAAC-OS filmobserved in a direction substantially perpendicular to the samplesurface (plan-view TEM image), metal atoms are arranged in a triangularor hexagonal configuration in the crystal parts. However, there is noregularity of arrangement of metal atoms between different crystalparts.

FIG. 11A is a cross-sectional TEM image of a CAAC-OS film. FIG. 11B is across-sectional TEM image obtained by enlarging the image of FIG. 11A.In FIG. 11B, atomic arrangement is highlighted for easy understanding.

FIG. 11C is Fourier transform images of regions each surrounded by acircle (with a diameter of approximately 4 nm) between A and O andbetween O and A′ in FIG. 11A. C-axis alignment can be observed in eachregion in FIG. 11C. The c-axis direction between A and O is differentfrom that between O and A′, which indicates that a grain in the regionbetween A and O is different from that between O and A′. In addition,between A and O, the angle of the c-axis changes gradually andcontinuously from 14.3° to 16.6° to 26.4°. Similarly, between O and A′,the angle of the c-axis changes gradually and continuously from −18.3°to −17.6° to −15.9°.

In an electron diffraction pattern of the CAAC-OS film, spots (brightspots) indicating alignment are shown. For example, when electrondiffraction with an electron beam having a diameter of 1 nm to 30 nm,for example (such electron diffraction is also referred to as nanobeamelectron diffraction) is performed on the top surface of the CAAC-OSfilm, spots are observed (see FIG. 12A).

From the results of the cross-sectional TEM image and the plan-view TEMimage, alignment is found in the crystal parts of the CAAC-OS film.

Most of the crystal parts included in the CAAC-OS film each fit inside acube whose one side is less than 100 nm. Thus, there is a case where acrystal part included in the CAAC-OS film fits inside a cube whose oneside is less than 10 nm, less than 5 nm, or less than 3 nm. Note thatwhen a plurality of crystal parts included in the CAAC-OS film areconnected to each other, one large crystal region is formed in somecases. For example, a crystal region with an area of 2500 nm² or more, 5μm² or more, or 1000 μm² or more is observed in some cases in theplan-view TEM image.

A CAAC-OS film is subjected to structural analysis with an X-raydiffraction (XRD) apparatus. For example, when the CAAC-OS filmincluding an InGaZnO₄ crystal is analyzed by an out-of-plane method, apeak appears frequently at a diffraction angle (2θ) of around 31°. Thispeak is derived from the (009) plane of the InGaZnO₄ crystal, whichindicates that crystals in the CAAC-OS film have c-axis alignment, andthat the c-axes are aligned in a direction substantially perpendicularto the formation surface or the top surface of the CAAC-OS film.

On the other hand, when the CAAC-OS film is analyzed by an in-planemethod in which an X-ray enters a sample in a direction substantiallyperpendicular to the c-axis, a peak appears frequently at 2θ of around56°. This peak is derived from the (110) plane of the InGaZnO₄ crystal.Here, analysis (φ scan) is performed under conditions where the sampleis rotated around a normal vector of a sample surface as an axis (φaxis) with 2θ fixed at around 56°. In the case where the sample is asingle crystal oxide semiconductor film of InGaZnO₄, six peaks appear.The six peaks are derived from crystal planes equivalent to the (110)plane. On the other hand, in the case of a CAAC-OS film, a peak is notclearly observed when φ scan is performed with 2θ fixed at around 56°.

According to the above results, in the CAAC-OS film, while thedirections of a-axes and b-axes are irregularly oriented between crystalparts, the c-axes are aligned in a direction parallel to a normal vectorof a formation surface or a normal vector of a top surface. Thus, eachmetal atom layer arranged in a layered manner observed in thecross-sectional TEM image corresponds to a plane parallel to the a-bplane of the crystal.

Note that the crystal part is formed concurrently with deposition of theCAAC-OS film or is formed through crystallization treatment such as heattreatment. As described above, the c-axis of the crystal is aligned in adirection parallel to a normal vector of a formation surface or a normalvector of a top surface. Thus, for example, when the shape of theCAAC-OS film is changed by etching or the like, the c-axis of thecrystal might not be necessarily parallel to a normal vector of aformation surface or a normal vector of a top surface of the CAAC-OSfilm.

Furthermore, distribution of c-axis aligned crystal parts in the CAAC-OSfilm is not necessarily uniform. For example, in the case where crystalgrowth leading to the CAAC-OS film occurs from the vicinity of the topsurface of the film, the crystallinity in the vicinity of the topsurface is higher than that in the vicinity of the formation surface insome cases. Moreover, when an impurity is added to the CAAC-OS film, aregion to which the impurity is added is altered, and the proportion ofthe c-axis aligned crystal parts in the CAAC-OS film sometimes variesdepending on regions.

When the CAAC-OS film with an InGaZnO₄ crystal is analyzed by anout-of-plane method, a peak may also be observed at 2θ of around 36° aswell as at 2θ of around 31°. The peak at 2θ of around 36° indicates thata crystal having no c-axis alignment is included in part of the CAAC-OSfilm. It is preferable that in the CAAC-OS film, a peak appear at 2θ ofaround 310 and a peak not appear at 2θ of around 36°.

The CAAC-OS film is an oxide semiconductor film having low impurityconcentration. The impurity is an element other than the main componentsof the oxide semiconductor film, such as hydrogen, carbon, silicon, or atransition metal element. In particular, an element that has higherbonding strength to oxygen than a metal element included in the oxidesemiconductor film, such as silicon, disturbs the atomic arrangement ofthe oxide semiconductor film by depriving the oxide semiconductor filmof oxygen and causes a decrease in crystallinity. A heavy metal such asiron or nickel, argon, carbon dioxide, or the like has a large atomicradius (molecular radius), and thus disturbs the atomic arrangement ofthe oxide semiconductor film and causes a decrease in crystallinity whenit is contained in the oxide semiconductor film. The impurity containedin the oxide semiconductor film might serve as a carrier trap or acarrier generation source.

The CAAC-OS film is an oxide semiconductor film having a low density ofdefect states. In some cases, oxygen vacancies in the oxidesemiconductor film serve as carrier traps or serve as carrier generationsources when hydrogen is captured therein.

The state in which the impurity concentration is low and the density ofdefect states is low (the number of oxygen vacancies is small) isreferred to as a “highly purified intrinsic” or “substantially highlypurified intrinsic” state. A highly purified intrinsic or substantiallyhighly purified intrinsic oxide semiconductor film has few carriergeneration sources, and thus can have a low carrier density.Consequently, a transistor including such an oxide semiconductor filmrarely has negative threshold voltage (rarely has normally-oncharacteristics). The highly purified intrinsic or substantially highlypurified intrinsic oxide semiconductor film has few carrier traps;therefore, the transistor including the oxide semiconductor film haslittle variation in electrical characteristics and high reliability.Electric charge trapped by the carrier traps in the oxide semiconductorfilm takes a long time to be released and might behave like fixedelectric charge. Thus, the transistor including an oxide semiconductorfilm having high impurity concentration and a high density of defectstates has unstable electrical characteristics in some cases.

With the use of the CAAC-OS film in a transistor, variation in theelectrical characteristics of the transistor due to irradiation withvisible light or ultraviolet light is small.

Next, a microcrystalline oxide semiconductor film is described.

In an image obtained with the TEM, crystal parts cannot be found clearlyin the microcrystalline oxide semiconductor film in some cases. In mostcases, a crystal part in the microcrystalline oxide semiconductor filmranges from 1 nm to 100 nm or from 1 nm to 10 nm. A microcrystal with asize in the range of 1 nm to 10 nm or of 1 nm to 3 nm is specificallyreferred to as nanocrystal (nc). An oxide semiconductor film includingnanocrystal is referred to as a nanocrystalline oxide semiconductor(nc-OS) film. In a TEM image of the nc-OS film, a grain boundary cannotbe found clearly in some cases.

In the nc-OS film, a microscopic region (e.g., a region with a sizeranging from 1 nm to 10 nm, in particular, from 1 nm to 3 nm) has aperiodic atomic order. There is no regularity of crystal orientationbetween different crystal parts in the nc-OS film; thus, the orientationof the whole film is not observed. Consequently, in some cases, thenc-OS film cannot be distinguished from an amorphous oxide semiconductorfilm depending on an analysis method. For example, when the nc-OS filmis subjected to structural analysis by an out-of-plane method with anXRD apparatus using an X-ray having a diameter larger than that of acrystal part, a peak showing a crystal plane does not appear. Adiffraction pattern like a halo pattern appears in a selected-areaelectron diffraction pattern of the nc-OS film obtained by using anelectron beam having a probe diameter larger than the diameter of acrystal part (e.g., having a probe diameter of 50 nm or larger).Meanwhile, spots are shown in a nanobeam electron diffraction pattern ofthe nc-OS film obtained by using an electron beam having a probediameter close to or smaller than the diameter of a crystal part.Furthermore, in a nanobeam electron diffraction pattern of the nc-OSfilm, regions with high luminance in a circular (ring) pattern aresometimes shown. Also in a nanobeam electron diffraction pattern of thenc-OS film, a plurality of spots are sometimes shown in a ring-likeregion (see FIG. 12B).

The nc-OS film is an oxide semiconductor film that has higher regularitythan an amorphous oxide semiconductor film, and therefore has a lowerdensity of defect states than an amorphous oxide semiconductor film.However, there is no regularity of crystal orientation between differentcrystal parts in the nc-OS film; hence, the nc-OS film has a higherdensity of defect states than the CAAC-OS film.

Note that an oxide semiconductor film may be a stacked film includingtwo or more films of an amorphous oxide semiconductor film, amicrocrystalline oxide semiconductor film, and a CAAC-OS film, forexample.

In the case where the oxide semiconductor film has a plurality ofstructures, the structures can be analyzed using nanobeam electrondiffraction in some cases.

FIG. 12C illustrates a transmission electron diffraction measurementapparatus that includes an electron gun chamber 70, an optical system 72below the electron gun chamber 70, a sample chamber 74 below the opticalsystem 72, an optical system 76 below the sample chamber 74, anobservation chamber 80 below the optical system 76, a camera 78installed in the observation chamber 80, and a film chamber 82 below theobservation chamber 80. The camera 78 is provided to face toward theinside of the observation chamber 80. Note that the film chamber 82 isnot necessarily provided.

FIG. 12D illustrates an internal structure of the transmission electrondiffraction measurement apparatus in FIG. 12C. In the transmissionelectron diffraction measurement apparatus, a substance 88 that ispositioned in the sample chamber 74 is irradiated with electrons emittedfrom an electron gun installed in the electron gun chamber 70 throughthe optical system 72. The electrons that have passed through thesubstance 88 enter a fluorescent plate 92 installed in the observationchamber 80 through the optical system 76. A pattern depending on theintensity of the incident electrons appears in the fluorescent plate 92,so that the transmission electron diffraction pattern can be measured.

The camera 78 is installed to face the fluorescent plate 92 and can takean image of a pattern appearing in the fluorescent plate 92. An angleformed by an upper surface of the fluorescent plate 92 and a straightline that passes through the center of a lens of the camera 78 and thecenter of the fluorescent plate 92 ranges from 15° to 80°, from 30° to75°, or from 45° to 70°, for example. As the angle becomes smaller,distortion of the transmission electron diffraction pattern taken by thecamera 78 becomes larger. Note that if the angle is obtained in advance,the distortion of an obtained transmission electron diffraction patterncan be corrected. The film chamber 82 may be provided with the camera78. For example, the camera 78 may be set in the film chamber 82 so asto be opposite to the incident direction of electrons 84. In this case,a transmission electron diffraction pattern with less distortion can betaken from the rear surface of the fluorescent plate 92.

A holder for fixing the substance 88 that is a sample is provided in thesample chamber 74. The holder transmits electrons passing through thesubstance 88. The holder may have, for example, a function of moving thesubstance 88 in the direction of the X, Y, and Z axes. The movementfunction of the holder may have an accuracy of moving the substance inthe range of, for example, 1 nm to 10 nm, 5 nm to 50 nm, 10 nm to 100nm, 50 nm to 500 nm, and 100 nm to 1 μm. The range is preferablydetermined to be an optimal range for the structure of the substance 88.

Next, a method for measuring a transmission electron diffraction patternof a substance by the aforementioned transmission electron diffractionmeasurement apparatus will be described.

For example, changes in the structure of a substance can be observed bychanging the irradiation position of the electrons 84 that are ananobeam on the substance (or by scanning) as illustrated in FIG. 12D.At this time, when the substance 88 is a CAAC-OS film, a diffractionpattern such as one shown in FIG. 12A is observed. When the substance 88is an nc-OS film, a diffraction pattern such as one shown in FIG. 12B isobserved.

Even when the substance 88 is a CAAC-OS film, a diffraction patternsimilar to that of an nc-OS film or the like is partly observed in somecases. Therefore, the quality of a CAAC-OS film can be sometimesrepresented by the proportion of a region where a diffraction pattern ofa CAAC-OS film is observed in a predetermined area (also referred to asproportion of CAAC (c-axis aligned crystal)). In a high-quality CAAC-OSfilm, for example, the proportion of CAAC is 50% or higher, preferably80% or higher, further preferably 90% or higher, still furtherpreferably 95% or higher. Note that a region where a diffraction patterndifferent from that of a CAAC-OS film is observed is referred to as theproportion of non-CAAC.

For example, transmission electron diffraction patterns were obtained byscanning a top surface of a sample including a CAAC-OS film obtainedjust after deposition (represented as “as-sputtered”) and a top surfaceof a sample including a CAAC-OS subjected to heat treatment at 450° C.in an atmosphere containing oxygen. Here, the proportion of CAAC wasobtained in such a manner that diffraction patterns were observed byscanning for 60 seconds at a rate of 5 nm/s and the obtained diffractionpatterns were converted into still images every 0.5 seconds. As anelectron beam, a nanobeam with a probe diameter of 1 nm was used. Theabove measurement was performed on six samples. The proportion of CAACwas calculated using the average value of the six samples.

FIG. 13A shows the proportion of CAAC in each sample. The proportion ofCAAC of the as-sputtered CAAC-OS film was 75.7% (the proportion ofnon-CAAC was 24.3%). The proportion of CAAC of the CAAC-OS filmsubjected to the heat treatment at 450° C. was 85.3% (the proportion ofnon-CAAC was 14.7%). These results show that the proportion of CAACobtained after the heat treatment at 450° C. is higher than thatobtained just after the deposition. That is, heat treatment at a hightemperature (e.g., 400° C. or higher) reduces the proportion of non-CAAC(increases the proportion of CAAC). The above results also indicate thatthe CAAC-OS film can have a high proportion of CAAC even when thetemperature of the heat treatment is lower than 500° C.

Here, most of diffraction patterns different from that of a CAAC-OS filmwere similar to that of an nc-OS film. Furthermore, an amorphous oxidesemiconductor film was not observed in the measurement region.Therefore, the above results suggest that the region having a structuresimilar to that of an nc-OS film is rearranged by heat treatment owingto the influence of the structure of the adjacent region, whereby theregion becomes CAAC.

FIGS. 13B and 13C are plan-view TEM images of the as-sputtered CAAC-OSfilm and the CAAC-OS film subjected to the heat treatment at 450° C.,respectively. Comparison between FIGS. 13B and 13C shows that theCAAC-OS film subjected to the heat treatment at 450° C. has more uniformfilm quality. That is, heat treatment at a high temperature improves thefilm quality of the CAAC-OS film.

With such a measurement method, the structure of an oxide semiconductorfilm having a plurality of structures can be analyzed in some cases.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 4

In this embodiment, an example of a cross-sectional structure of atransistor used in a semiconductor device of one embodiment of thedisclosed invention will be described with reference to drawings.

FIG. 14 illustrates an example of part of the cross-sectional structureof the semiconductor device in one embodiment of the present invention.FIG. 14 illustrates the transistor 11 and the transistor 12 shown inFIG. 2.

In this embodiment, the transistor 12 is formed in a single crystalsilicon substrate, and the transistor 11 including a semiconductor layercontaining an oxide semiconductor is formed above the transistor 12. Thetransistor 12 may include a thin semiconductor layer of silicon,germanium, or the like in an amorphous, microcrystalline,polycrystalline, or single crystal state.

When the transistor 12 is formed using a thin silicon film, any of thefollowing can be used, for example: amorphous silicon formed bysputtering or vapor phase growth such as plasma-enhanced CVD;polycrystalline silicon obtained by crystallization of amorphous siliconby laser annealing or the like; and single crystal silicon obtained byseparation of a surface portion of a single crystal silicon wafer byimplantation of hydrogen ions or the like into the silicon wafer.

FIG. 14 illustrates a structure where the transistor 11 is formed abovethe transistor 12. With the structure in FIG. 14, a channel formationregion of the transistor 11 and a channel formation region of thetransistor 12 can be provided to overlap with each other; thus, thelayout area of a semiconductor device can be small. In thecross-sectional structure in FIG. 14, the channel length L of thetransistor 11 is smaller than that of the transistor 12. Since the OStransistor has high withstand voltage, even such a structure results ina semiconductor device having the transistor with high withstand voltageand high reliability.

In FIG. 14, the p-channel transistor 12 is formed in a semiconductorsubstrate 800.

The semiconductor substrate 800 can be, for example, an n-type or p-typesilicon substrate, germanium substrate, silicon germanium substrate, orcompound semiconductor substrate (e.g., GaAs substrate, InP substrate,GaN substrate, SiC substrate, GaP substrate, GaInAsP substrate, or ZnSesubstrate). FIG. 14 illustrates an example where an p-type singlecrystal silicon substrate is used.

The transistor 12 is electrically isolated from another transistor by anelement isolation insulating film 801. The element isolation insulatingfilm 801 can be formed by a local oxidation of silicon (LOCOS) method, atrench isolation method, or the like.

Specifically, the transistor 12 includes impurity regions 802 and 803that are formed in the semiconductor substrate 800 and function as asource region and a drain region, a gate electrode 804, and a gateinsulating film 805 provided between the semiconductor substrate 800 andthe gate electrode 804. The gate electrode 804 overlaps a channelformation region formed between the impurity regions 802 and 803 withthe gate insulating film 805 positioned between the gate electrode 804and the channel formation region.

An insulating film 809 is provided over the transistor 12. Openings areformed in the insulating film 809. Wirings 810 and 811 that are incontact with the impurity regions 802 and 803, respectively, are formedin the openings.

The wiring 810 is connected to a wiring 816 formed over the insulatingfilm 809. The wiring 811 is connected to a wiring 817 formed over theinsulating film 809.

An insulating film 820 is formed over the wirings 816 and 817.

In FIG. 14, the transistor 11 is formed over the insulating film 820.

The transistor 11 includes, over the insulating film 820, asemiconductor film 830 containing an oxide semiconductor, conductivefilms 832 and 833 that are positioned over the semiconductor film 830and function as a source electrode and a drain electrode, a gateinsulating film 831 over the semiconductor film 830 and the conductivefilms 832 and 833, and a gate electrode 834 that is positioned over thegate insulating film 831 and overlaps the semiconductor film 830 betweenthe conductive films 832 and 833.

An insulating film 841 is provided over the transistor 111.

The semiconductor film 830 is not limited to a single oxidesemiconductor film and may be stacked oxide semiconductor films. FIG.15A illustrates an example of the transistor 11 in which thesemiconductor film 830 has a three-layer structure.

The transistor 11 illustrated in FIG. 15A includes the semiconductorfilm 830 over the insulating film 820 and the like, the conductive films832 and 833 electrically connected to the semiconductor film 830, thegate insulating film 831, and the gate electrode 834 provided over thegate insulating film 831 so as to overlap the semiconductor film 830.

As the semiconductor film 830 in the transistor 11, oxide semiconductorlayers 830 a to 830 c are stacked sequentially from the insulating film820 side.

The oxide semiconductor layers 830 a and 830 c are each an oxide filmthat contains at least one of metal elements contained in the oxidesemiconductor layer 830 b. The energy at the bottom of the conductionband of the oxide semiconductor layers 830 a and 830 c is closer to avacuum level than that of the oxide semiconductor layer 830 b by 0.05 eVor more, 0.07 eV or more, 0.1 eV or more, or 0.15 eV or more and 2 eV orless, 1 eV or less, 0.5 eV or less, or 0.4 eV or less. The oxidesemiconductor layer 830 b preferably contains at least indium toincrease carrier mobility.

As illustrated in FIG. 15B, the oxide semiconductor layer 830 c may beprovided over the conductive films 832 and 833 so as to overlap with thegate insulating film 831.

The cross-sectional structure in FIG. 14 enables a semiconductor deviceto have a smaller circuit area than a semiconductor device using only Sitransistors with large channel length L. In the semiconductor devicewith the cross-sectional structure in FIG. 14, the transistors can havehigh withstand voltage without increasing in size. As a result, a highlyreliable semiconductor device can be provided.

In the case where the mobility of a Si transistor is higher than that ofan OS transistor, the channel width W of the OS transistor is set largerthan that of the Si transistor.

This embodiment can be implemented in appropriate combination with anyof the other embodiments.

Embodiment 5

Although the conductive film and the semiconductor film described in theabove embodiments can be formed by sputtering, they may be formed byanother method, for example, a thermal CVD method. Examples of a thermalCVD method include metal organic chemical vapor deposition (MOCVD) andatomic layer deposition (ALD).

A thermal CVD method has an advantage that no defect due to plasmadamage is generated because it does not utilize plasma for forming afilm.

Deposition by a thermal CVD method may be performed in such a mannerthat a source gas and an oxidizer are supplied to a chamber at a time,the pressure in the chamber is set to an atmospheric pressure or areduced pressure, and reaction is caused in the vicinity of a substrateor over the substrate.

Deposition by an ALD method may be performed in such a manner that thepressure in a chamber is set to an atmospheric pressure or a reducedpressure, source gases for reaction are sequentially introduced into thechamber, and then the sequence of the gas introduction is repeated. Forexample, two or more kinds of source gases are sequentially supplied tothe chamber by switching respective switching valves (also referred toas high-speed valves). For instance, a first source gas is introduced,an inert gas (e.g., argon or nitrogen) or the like is introduced at thesame time as or after the introduction of the first gas so that thesource gases are not mixed, and then a second source gas is introduced.Note that in the case where the first source gas and the inert gas areintroduced at a time, the inert gas serves as a carrier gas, and theinert gas may also be introduced at the same time as the introduction ofthe second source gas. Alternatively, the second source gas may beintroduced after the first source gas is exhausted by vacuum evacuationinstead of the introduction of the inert gas. The first source gas isadsorbed on the surface of a substrate to form a first layer, and then,the second source gas is introduced to react with the first layer. As aresult, a second layer is stacked over the first layer, so that a thinfilm is formed. The sequence of the gas introduction is repeatedmultiple times until a desired thickness is obtained, whereby a thinfilm with excellent step coverage can be formed. The thickness of thethin film can be adjusted by the number of repetitions of the sequenceof the gas introduction; therefore, an ALD method makes it possible toaccurately adjust a thickness and thus is suitable for manufacturing aminute FET.

The conductive film and the semiconductor film described in the aboveembodiments can be formed by thermal CVD such as MOCVD or ALD. Forexample, trimethylindium, trimethylgallium, and dimethylzinc are used toform an In—Ga—Zn—O film. Note that the chemical formula oftrimethylindium is In(CH₃)₃. The chemical formula of trimethylgallium isGa(CH₃)₃. The chemical formula of dimethylzinc is Zn(CH₃)₂. Withoutlimitation to the above combination, triethylgallium (chemical formula:Ga(C₂H₅)₃) can be used instead of trimethylgallium, and diethylzinc(chemical formula: Zn(C₂H₅)₂) can be used instead of dimethylzinc.

For example, when a tungsten film is formed with a deposition apparatususing ALD, a WF₆ gas and a B₂H₆ gas are sequentially introduced multipletimes to form an initial tungsten film, and then a WF₆ gas and an H₂ gasare introduced at a time, so that a tungsten film is formed. Note that aSiH₄ gas may be used instead of a B₂H₆ gas.

When an oxide semiconductor film, for example, an In—Ga—Zn—O film isformed with a deposition apparatus using ALD, an In(CH₃)₃ gas and an O₃gas are sequentially introduced multiple times to form an In—O layer, aGa(CH₃)₃ gas and an O₃ gas are introduced at a time to form a Ga—Olayer, and then a Zn(CH₃)₂ gas and an O₃ gas are introduced at a time toform a Zn—O layer. Note that the order of these layers is not limited tothis example. A mixed compound layer such as an In—Ga—O layer, anIn—Zn—O layer, or a Ga—Zn—O layer may be formed by mixing of thesegases. Although an H₂O gas obtained by bubbling with an inert gas suchas Ar may be used instead of an O₃ gas, it is preferable to use an O₃gas, which does not contain H. Furthermore, an In(C₂H₃)₃ gas may be usedinstead of an In(CH₃)₃ gas. A Ga(C₂H₅)₃ gas may be used instead of aGa(CH₃)₃ gas. Moreover, a Zn(CH₃)₂ gas may be used.

The structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 6

In this embodiment, an application example of the semiconductor devicedescribed in the foregoing embodiments to an electronic component,application examples of the electronic component to a display module, anapplication example of the display module, and application examples ofan electronic device will be described with reference to FIGS. 16A and16B, FIGS. 17A and 17B, FIG. 18, and FIGS. 19A to 19E.

Application Example to Electronic Component

FIG. 6A shows an example where the semiconductor device described in theforegoing embodiment is used to make an electronic component. Note thatan electronic component is also referred to as semiconductor package orIC package. For the electronic component, there are various standardsand names corresponding to the direction of terminals or the shape ofterminals; hence, one example of the electronic component will bedescribed in this embodiment.

A semiconductor device including the transistors illustrated in FIG. 14of Embodiment 4 is completed by integrating detachable components on aprinted circuit board through the assembly process (post-process).

The post-process can be completed through steps shown in FIG. 16A.Specifically, after an element substrate obtained in the wafer processis completed (Step S1), a back surface of the substrate is ground (StepS2). The substrate is thinned in this step to reduce warpage or the likeof the substrate in the wafer process and to reduce the size of thecomponent itself.

A dicing step of grinding the back surface of the substrate to separatethe substrate into a plurality of chips is performed. Then, a diebonding step of individually picking up separate chips to be mounted onand bonded to an interposer is performed (Step S3). To bond a chip andan interposer in the die bonding step, resin bonding, tape-automatedbonding, or the like is selected as appropriate depending on products.

Next, wire bonding for electrically connecting a wire of the interposerand an electrode on a chip through a metal wire is performed (Step S4).As a metal wire, a silver wire or a gold wire can be used. For wirebonding, ball bonding or wedge bonding can be employed.

A wire-bonded chip is subjected to a molding step of scaling the chipwith an epoxy resin or the like (Step S5). With the molding step, theinside of the electronic component is filled with a resin, therebyreducing damage to the circuit portion and the wire embedded in thecomponent caused by external mechanical force as well as reducingdeterioration of characteristics due to moisture or dust.

Subsequently, printing process (marking) is performed on a surface ofthe package (Step S6). Then, through a final test step (Step S7), theelectronic component is completed (Step S8).

Since the electronic component described above includes thesemiconductor device described in the foregoing embodiment, it ispossible to obtain a small and highly reliable electronic component.

FIG. 16B is a schematic cross-sectional view of a completed electroniccomponent. In an electronic component 700 illustrated in FIG. 16B, asemiconductor device 701 is provided on a surface of an interposer 702.The semiconductor device 701 is connected to a wiring on the surface ofthe interposer 702 via a wire 705 to be electrically connected to a bumpterminal 706 provided on the back surface of the interposer 702. Thesemiconductor device 701 over the interposer 702 is sealed by a package703 with a space between the interposer 702 and the package 703 filledwith an epoxy resin 704.

The electronic component 700 in FIG. 16B is mounted on a flexibleprinted circuit (FPC) or a display panel, for example.

Examples of Mounting Electronic Component on Display Panel

Next, examples of a display panel with the semiconductor device used fora source driver IC will be described with reference to FIGS. 17A and17B.

FIG. 17A illustrates an example where a source driver 712 and gatedrivers 712A and 712B are provided around a display portion 711 and asource driver IC 714 is mounted on a substrate 713 as the source driver712.

The source driver IC 714 is mounted on a substrate 713 using ananisotropic conductive adhesive and an anisotropic conductive film.

The source driver IC 714 is connected to an external circuit board 716via an FPC 715.

FIG. 17B illustrates an example where the source driver 712 and the gatedrivers 712A and 712B are provided around the display portion 711 andthe source driver IC 714 is mounted on the FPC 715 as the source driver712.

Mounting the source driver IC 714 on the FPC 715 allows a larger displayportion 711 to be provided over the substrate 713, resulting in anarrower frame.

Application Example of Display Module

Next, an application example of a display module using the display panelillustrated in FIG. 17A or FIG. 17B will be described with reference toFIG. 18.

In a display module 8000 illustrated in FIG. 18, a touch panel 8004connected to an FPC 8003, a display panel 8006 connected to an FPC 8005,a backlight unit 8007, a frame 8009, a printed circuit board 8010, and abattery 8011 are provided between an upper cover 8001 and a lower cover8002. Note that the backlight unit 8007, the battery 8011, the touchpanel 8004, and the like are not provided in some cases.

The display panel illustrated in FIG. 17A or FIG. 17B can be used as thedisplay panel 8006 in FIG. 18.

The shape and size of the upper cover 8001 and the lower cover 8002 canbe changed as appropriate in accordance with the size of the touch panel8004 and the display panel 8006.

The touch panel 8004 can be a resistive touch panel or a capacitivetouch panel and can be formed to overlap with the display panel 8006. Itis also possible to provide a touch panel function for a countersubstrate (sealing substrate) of the display panel 8006. Alternatively,a photosensor may be provided in each pixel of the display panel 8006 toform an optical touch panel. An electrode for a touch sensor may beprovided in each pixel of the display panel 8006 so that a capacitivetouch panel is obtained.

The backlight unit 8007 includes a light source 8008. The light source8008 may be provided at an end portion of the backlight unit 8007 and alight diffusing plate may be used.

The frame 8009 protects the display panel 8006 and functions as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed circuit board 8010. The frame 8009 may alsofunction as a radiator plate.

The printed circuit board 8010 is provided with a power supply circuitand a signal processing circuit for outputting a video signal and aclock signal. As a power source for supplying power to the power supplycircuit, an external commercial power source or a separate power sourceusing the battery 8011 may be used. The battery 8011 can be omitted inthe case of using a commercial power source.

The display module 8000 may be additionally provided with a polarizingplate, a retardation plate, a prism sheet, or the like.

Application Examples of Electronic Component to Electronic Device

Next, an electronic device having a display panel including the aboveelectronic component will be described. Examples of the electronicdevice include a computer, a portable information appliance (including amobile phone, a portable game machine, and an audio reproducing device),electronic paper, a television device (also referred to as television ortelevision receiver), and a digital video camera.

FIG. 19A illustrates a portable information appliance that includes ahousing 901, a housing 902, a first display portion 903 a, a seconddisplay portion 903 b, and the like. At least one of the housings 901and 902 is provided with the electronic component including thesemiconductor device of the foregoing embodiment. It is thus possible toobtain a small and highly reliable portable information appliance.

The first display portion 903 a is a panel having a touch inputfunction, and for example, as illustrated in the left of FIG. 19A, whichof “touch input” and “keyboard input” is performed can be selected by aselection button 904 displayed on the first display portion 903 a. Sinceselection buttons with a variety of sizes can be displayed, theinformation appliance can be easily used by people of any generation.For example, when “keyboard input” is selected, a keyboard 905 isdisplayed on the first display portion 903 a as illustrated in the rightof FIG. 19A. Thus, letters can be input quickly by key input as in aconventional information appliance, for example.

One of the first display portion 903 a and the second display portion903 b can be detached from the portable information appliance as shownin the right of FIG. 19A. Providing the second display portion 903 bwith a touch input function makes the information appliance convenientbecause a weight to carry around can be further reduced and theinformation appliance can operate with one hand while the other handsupports the housing 902.

The portable information appliance in FIG. 19A can be equipped with afunction of displaying a variety of information (e.g., a still image, amoving image, and a text image); a function of displaying a calendar, adate, the time, or the like on the display portion; a function ofoperating or editing information displayed on the display portion; afunction of controlling processing by various kinds of software(programs); and the like. Furthermore, an external connection terminal(e.g., an earphone terminal or a USB terminal), a recording mediuminsertion portion, and the like may be provided on the back surface orthe side surface of the housing.

The portable information appliance illustrated in FIG. 19A may transmitand receive data wirelessly. Through wireless communication, desiredbook data or the like can be purchased and downloaded from an e-bookserver.

Furthermore, the housing 902 in FIG. 19A may be equipped with anantenna, a microphone function, and a wireless communication function tobe used as a mobile phone.

FIG. 19B illustrates an e-book reader 910 including electronic paper.The e-book reader 910 has two housings 911 and 912. The housing 911 andthe housing 912 are provided with a display portion 913 and a displayportion 914, respectively. The housings 911 and 912 are connected by ahinge 915 and can be opened and closed with the hinge 915 as an axis.The housing 911 is provided with a power switch 916, an operation key917, a speaker 918, and the like. The electronic component including thesemiconductor device of the foregoing embodiment is provided in at leastone of the housings 911 and 912. It is thus possible to obtain a smalland highly reliable e-book reader.

FIG. 19C illustrates a television device including a housing 921, adisplay portion 922, a stand 923, and the like. The television devicecan be controlled by a switch of the housing 921 and a separate remotecontroller 924. The electronic component including the semiconductordevice of the foregoing embodiment is mounted on the housing 921 and theremote controller 924. Thus, it is possible to obtain a small and highlyreliable television device.

FIG. 19D illustrates a smartphone in which a main body 930 is providedwith a display portion 931, a speaker 932, a microphone 933, anoperation button 934, and the like. The electronic component includingthe semiconductor device of the foregoing embodiment is provided in themain body 930. It is thus possible to obtain a small and highly reliablesmartphone.

FIG. 19E illustrates a digital camera including a main body 941, adisplay portion 942, an operation switch 943, and the like. Theelectronic component including the semiconductor device of the foregoingembodiment is provided in the main body 941. Consequently, it ispossible to obtain a small and highly reliable digital camera.

As described above, the electronic device shown in this embodimentincorporates the electronic component including the semiconductor deviceof the foregoing embodiment, thereby being reduced in size and havinghigh reliability.

This application is based on Japanese Patent Application serial no.2014-044471 filed with Japan Patent Office on Mar. 7, 2014, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A semiconductor device comprising: a firstcircuit configured to generate voltages; a second circuit configured toconvert a first signal into a second signal; and a third circuitconfigured to amplify the second signal, wherein the second circuitcomprising first to sixth transistors, wherein one of a source and adrain of the first transistor, one of a source and a drain of the secondtransistor, one of a source and a drain of the third transistor, and oneof a source and a drain of the fourth transistor are electricallyconnected to the first circuit, wherein one of a source and a drain ofthe fifth transistor is electrically connected to the other of thesource and the drain of the first transistor and the other of the sourceand the drain of the second transistor, wherein one of a source and adrain of the sixth transistor is electrically connected to the other ofthe source and the drain of the third transistor and the fourthtransistor, wherein the other of the source and the drain of the fifthtransistor and the other of the source and the drain of the sixthtransistor are electrically connected to the third circuit, wherein agate of the first transistor and a gate of the third transistor areelectrically connected to a first wiring, wherein a gate of the secondtransistor and a gate of the fourth transistor are electricallyconnected to a second wiring, wherein a gate of the fifth transistor iselectrically connected to a third wiring, and wherein each of the first,second, and fifth transistors comprises a semiconductor layer comprisingan oxide semiconductor.
 2. The semiconductor device according to claim1, wherein the first to third wirings are configured to transmitdifferent voltages.
 3. The semiconductor device according to claim 1,further comprising: a fourth circuit configured to boost a voltage ofthe first signal, wherein the fourth circuit is electrically connectedto the gates of the first to sixth transistors.
 4. The semiconductordevice according to claim 1, wherein the oxide semiconductor comprisesIn, Ga, and Zn.
 5. The semiconductor device according to claim 1,wherein each of the third, fourth, and sixth transistors comprises asemiconductor layer comprising silicon.
 6. An electronic componentcomprising: the semiconductor device according to claim 1; and a bumpterminal electrically connected to the semiconductor device.
 7. Anelectronic device comprising: the electronic component according toclaim 6; and a display device.